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1 of 8© Boardworks Ltd 2010. 2 of 8© Boardworks Ltd 2010 Links to the current specifications AQA3.4.8 Amino acids: acid and base properties; proteins.

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Presentation on theme: "1 of 8© Boardworks Ltd 2010. 2 of 8© Boardworks Ltd 2010 Links to the current specifications AQA3.4.8 Amino acids: acid and base properties; proteins."— Presentation transcript:

1 1 of 8© Boardworks Ltd 2010

2 2 of 8© Boardworks Ltd 2010 Links to the current specifications AQA3.4.8 Amino acids: acid and base properties; proteins. EdexcelTopic 5.4 – Organic chemistry 5.4.2a Give examples of: i. molecules that contain amine and amide functional groups. ii. amino acids h Comment on the physical properties of polyamides in terms of hydrogen bonding i Describe and carry out, where appropriate, experiments to investigate the characteristic behaviour of amino acids. This is limited to: i. acidity and basicity and the formation of zwitterions. iv. formation of peptide groups in proteins by condensation polymerization. OCR4.2.1 Amino acids and chirality: amino acids; peptide formation and hydrolysis of proteins Polyesters and polyamides: condensation polymers; hydrolysis and degradable polymers.

3 3 of 8© Boardworks Ltd 2010 Proteins and amino acids Proteins are a diverse group of large and complex polymer molecules, made up of long chains of amino acids. The R group, also attached to the same carbon atom, can vary. There are 22 amino acids that are used to make proteins (proteinogenic). The simplest is glycine, where R = H. Amino acids contain both amine (NH 2 ) and carboxyl (COOH) functional groups. In alpha amino acids, these groups are attached to the same carbon atom. glycine (gly)

4 4 of 8© Boardworks Ltd 2010 Zwitterions

5 5 of 8© Boardworks Ltd 2010 Acid–base properties of amino acids The presence of a carboxyl group and an amine group mean that amino acids have both acidic and basic properties. NH 2 group acts as a base COOH acid group acts as an acid When acting as an acid, the COOH group loses a H + ion: When acting as a base, the NH 2 group gains a H + ion: H 2 NCHRCOOH + OH -  H 2 NCHRCOO - + H 2 OH 2 NCHRCOOH + H +  H 3 N + CHRCOOH

6 6 of 8© Boardworks Ltd 2010 Effect of pH on amino acids

7 7 of 8© Boardworks Ltd 2010 Peptide formation

8 8 of 8© Boardworks Ltd 2010 Hydrolysis of peptide bonds A peptide bond can be split by refluxing with hydrochloric acid. During hydrolysis, the water molecule adds across the peptide bond, forming a mixture of the two amino acids. Peptide links can also be broken using a solution of alkali, such as aqueous sodium hydroxide at above 100°C.


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